Conversion table creating device, storage medium storing conversion table creating program, and conversion table converting method

1. A conversion table creating device for creating a color conversion table for converting a set of first color data defined in a first color space, that is a uniform color space, to a set of second color data defined in a second color space different from the first color space, the conversion table creating device comprising: a first reference point setting unit that sets a plurality of first reference points that are uniformly distributed in the first color space, each of the plurality of first reference points being defined by a set of third color data that is defined in the first color space; a second reference point setting unit that sets a plurality of second reference points that are uniformly distributed in the second color space, each of the plurality of second reference points being defined by a set of fourth color data that is defined in the second color space; a color data setting unit that sets a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets; an identifying unit that identifies a single first reference point, that is closest to the fifth color data set for each of the second reference points; a calculation unit that calculates, for each of all the second reference points, a color difference between the fifth color data set for the each second reference point and the single first reference point that is identified by the identifying unit for the each second reference point; a determining unit that determines, for each of the single first reference points, a single fifth color data set that has the smallest color difference from the single first reference point among all the color differences that are calculated with respect to the single first reference point by the calculating unit; a registering unit that registers, at each of the single first reference points, the fourth color data set that is set in correspondence with the single fifth color data sets that is determined by the determining unit; a first judging unit; an updating unit; and an update performing unit that repeatedly performs an updating process for each of the single first reference points, wherein the update performing unit performs the updating process by controlling (1) the second reference point setting unit to further set a plurality of second reference points that are uniformly distributed in a subspace in the second color space, the subspace encompassing only a single one among the plurality of second reference points already set by the second reference point setting unit, the fourth color data set of the single second reference point being registered at the single first reference point, each of the plurality of second reference points in the subspace being defined by a set of fourth color data that is defined in the second color space; (2) the color data setting unit to set a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets of the second reference points in the subspace; (3) the calculation unit to calculate, for each of all the second reference points in the subspace, color differences between the fifth color data set for each second reference point in the subspace and the single first reference point, at which the fourth color data set of the single second reference point is registered; (4) the first judging unit to judge whether or not the smallest color difference among all the color differences that are calculated with respect to each of the second reference points in the subspace is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered; and (5) the updating unit to update, if the first judging unit judges that the smallest color difference among all the color differences is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered, the fourth color data set, that is already registered at the single first reference point, to the fourth color data set that is set in correspondence with the fifth color data set having the smallest color difference among all the color differences that are calculated with respect to the each second reference point in the subspace.

2. The conversion table creating device according to claim 1 , wherein the subspace is bounded by intermediate points between the single second reference point and other second reference points, that are already set by the second reference point setting unit adjacent to the single second reference point.

3. The conversion table creating device according to claim 1 , further comprising a second judging unit that judges whether or not the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the first reference point, at which the fourth color data set of the single second reference point is registered is greater than a prescribed target color difference, wherein the update performing unit performs the updating process if the second judging unit judges that the smallest color difference of the fifth color data set in correspondence with the fourth color data set of the single second reference point is greater than the prescribed target color difference.

4. The conversion table creating device according to claim 3 , wherein the update performing unit ends the updating process if the second judging unit judges that the smallest color difference of the fifth color data set in correspondence with the fourth color data set of the single second reference point is equal to or smaller than the prescribed target color difference.

5. The conversion table creating device according to claim 1 , wherein the update performing unit has a restriction on the number of times the updating process is repeated.

6. A computer-readable storage medium storing a computer-executable conversion table creating program for a conversion table creating device, the conversion table creating device creating a color conversion table for converting a set of first color data defined in a first color space, that is a uniform color space, to a set of second color data defined in a second color space different from the first color space, the conversion table creating program comprising: instructions for setting a plurality of first reference points that are uniformly distributed in the first color space, each of the plurality of first reference points being defined by a set of third color data that is defined in the first color space; instructions for setting a plurality of second reference points that are uniformly distributed in the second color space, each of the plurality of second reference points being defined by a set of fourth color data that is defined in the second color space; instructions for setting a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets; instructions for identifying a single first reference point, that is closest to the fifth color data set for each of the second reference points; instructions for calculating, for each of all the second reference points, a color difference between the fifth color data set for the each second reference point and the single first reference point that is identified in the identifying instructions for the each second reference point; instructions for determining, for each of the single first reference points, a single fifth color data set that has the smallest color difference from the single first reference point among all the color differences that are calculated with respect to the single first reference point in the calculating instructions; instructions for registering, at each of the single first reference points, the fourth color data set that is set in correspondence with the single fifth color data sets that is determined in the determining instructions; and instructions for repeatedly performing an updating process for each of the single first reference points, wherein the updating process is performed (1) to further set a plurality of second reference points that are uniformly distributed in a subspace in the second color space, the subspace encompassing only a single one among the plurality of second reference points already set in response to the instructions for setting the plurality of second reference points, the fourth color data set of the single second reference point being registered at the single first reference point, each of the plurality of second reference points in the subspace being defined by a set of fourth color data that is defined in the second color space; (2) to set a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets of the second reference points in the subspace; (3) to calculate, for each of all the second reference points in the subspace, color differences between the fifth color data set for each second reference point in the subspace and the single first reference point, at which the fourth color data set of the single second reference point is registered; (4) to judge whether or not the smallest color difference among all the color differences that are calculated with respect to each of the second reference points in the subspace is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered; and (5) to update, if the smallest color difference among all the color differences is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered, the fourth color data set, that is already registered at the single first reference point, to the fourth color data set that is set in correspondence with the fifth color data set having the smallest color difference among all the color differences that are calculated with respect to the each second reference point in the subspace.

7. A conversion table creating method for a conversion table creating device, the conversion table creating device creating a color conversion table for converting a set of first color data defined in a first color space, that is a uniform color space, to a set of second color data defined in a second color space different from the first color space, the conversion table creating method comprising: setting a plurality of first reference points that are uniformly distributed in the first color space, each of the plurality of first reference points being defined by a set of third color data that is defined in the first color space; setting a plurality of second reference points that are uniformly distributed in the second color space, each of the plurality of second reference points being defined by a set of fourth color data that is defined in the second color space; setting a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets; identifying a single first reference point, that is closest to the fifth color data set for each of the second reference points; calculating, using a personal computer, for each of all the second reference points, a color difference between the fifth color data set for the each second reference point and the single first reference point that is identified in the identifying instructions for the each second reference point; determining, for each of the single first reference points, a single fifth color data set that has the smallest color difference from the single first reference point among all the color differences that are calculated with respect to the single first reference point in the calculating instructions; registering, at each of the single first reference points, the fourth color data set that is set in correspondence with the single fifth color data sets that is determined in the determining instructions; and performing, using the personal computer, an updating process for each of the single first reference points repeatedly, wherein the updating process is performed (1) to further set a plurality of second reference points that are uniformly distributed in a subspace in the second color space, the subspace encompassing only a single one among the plurality of second reference points already set in response to the instructions for setting the plurality of second reference points, the fourth color data set of the single second reference point being registered at the single first reference point, each of the plurality of second reference points in the subspace being defined by a set of fourth color data that is defined in the second color space; (2) to set a plurality of sets of fifth color data that are defined in the first color space in one to one correspondence with the plurality of fourth color data sets of the second reference points in the subspace; (3) to calculate, for each of all the second reference points in the subspace, color differences between the fifth color data set for each second reference point in the subspace and the single first reference point, at which the fourth color data set of the single second reference point is registered; (4) to judge whether or not the smallest color difference among all the color differences that are calculated with respect to each of the second reference points in the subspace is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered; and (5) to update, if the smallest color difference among all the color differences is smaller than the color difference between the fifth color data set in correspondence with the fourth color data set of the single second reference point and the single first reference point, at which the fourth color data set of the single second reference point is registered, the fourth color data set, that is already registered at the single first reference point, to the fourth color data set that is set in correspondence with the fifth color data set having the smallest color difference among all the color differences that are calculated with respect to the each second reference point in the subspace.